Microscopic investigations on living animals are performed at various locations on the animal for purposes of basic research. In particular, the interaction of neurons following an applied external stimulus is investigated in various tissue layers in the brains of laboratory animals, e.g. mice. The speed with which the stimulus is transmitted, and the interconnections among the neurons, can supply valuable information that may lead to a better understanding of various brain diseases (Parkinson's, Alzheimer's, multiple sclerosis). It is also usual to perform surgical operations in which tissue is exposed and is continuously monitored microscopically, for example so that a change in blood flow can be observed (by measuring the flow rate) in peripheral tissues after the application of various medications.
In these investigations, the animal is tranquilized and the body part on which the tissue investigation is taking place is immobilized in a position suitable for microscopy. For investigations of the brain, the animal's head is appropriately immobilized under the microscope. Despite this immobilization, positional changes of the tissue with respect to the microscope can be brought about. The positional changes can be brought about on the one hand by a movement caused by or imparted to the animal. On the other hand, positional changes of the tissue being investigated can also result from movements of the animal's organs, in particular due to respiration and the animal's heartbeat and pulse. The changes in tissue position caused thereby generally do not represent a uniform movement. They can, however, be greater than the microscope's depth of field in the direction of the optical axis of the microscope; this is often the case at higher microscope magnifications or in the context of a confocal microscope. As a result, in a series of individual images of a tissue layer acquired by means of a camera on the microscope, some of the images are not sharp. These images are thus created during a time period in which the tissue, because of its movement, is not located at the microscope's focus. These unsharp images must then be identified within the overall image data set by visual inspection by a professional user, and discarded or deleted. This process is cumbersome and time-consuming. If a non-electronic camera is used, a large amount of unusable film material is moreover generated, which is unfavorable in terms of cost.
The sharp and unsharp microscope images created in time with the animal's movements are, of course, also disruptive when continuously viewing the tissue layer through the microscope. The same is also true for images acquired using an electronic camera with simultaneous visualization of the images on a monitor or display. With continuous observation, the alternately sharp and unsharp images quickly cause visual fatigue in the viewer.